1. Field of the Invention
The present invention relates to a gas shower unit for a semiconductor manufacturing apparatus. In particular, the invention relates to a gas shower unit used in a semiconductor manufacturing apparatus such as CVD apparatus, plasma CVD apparatus, etching apparatus and plasma etching apparatus for the purpose of uniformly supplying reactant gas to a semiconductor wafer.
2. Description of the Background Art
For etching of a semiconductor wafer surface or depositing of a film thereon, a method has been employed according to which gas for etching or for film deposition is supplied by means of batch processing to a large number of wafers held on racks, and then the wafers are heated as required from the outer periphery (hot wall method).
However, as requirements become severer for higher integration and speed of semiconductor devices, a problem arises of non-uniform etching and unequal quality of completed films due to difference in temperature and gas flow depending on the location in a semiconductor manufacturing apparatus. Then, another type of semiconductor manufacturing apparatus has gradually been used instead that employs single wafer processing in which a plurality of etching apparatuses and film deposition apparatuses are arranged side by side and wafers are transported automatically by a loader through the apparatuses where the wafers are processed one by one.
In the semiconductor manufacturing apparatus employing the single wafer processing, a semiconductor wafer is placed on the surface of a holder made of ceramics or metal. The wafer is secured onto the holder surface statically, mechanically, or by applying voltage to an electrode provided in the holder so as to fasten the wafer by an electrostatic force. The surface temperature of the semiconductor wafer held on the holder is precisely controlled in order to adjust the film deposition rate or etching rate in the process of CVD (Chemical Vapor Deposition), plasma CVD, etching, plasma etching or the like. For this temperature control, the wafer holder has a heater therein to heat the outermost surface of the holder and accordingly heat the semiconductor wafer by heat transfer. In order to cut the manufacturing cost of semiconductor devices, an attempt is made to increase the diameter of a semiconductor wafer and thus increase the number of semiconductor chips produced from one wafer. If the diameter of the semiconductor wafer is increased, it is more severely required to uniformly heat the outermost surface of the wafer holder in order to avoid different reaction environments in etching or film deposition within a semiconductor manufacturing apparatus.
Further, if reactant gas is merely supplied through a pipe attached to a chamber of the semiconductor manufacturing apparatus, gas does not uniformly flow through respective regions where the gas is directly and indirectly supplied respectively. As a result, the reactant gas has different concentrations on the surface of a semiconductor wafer. Control accordingly becomes difficult for realizing uniform etching or film deposition on the surface of the semiconductor wafer. Then, for the purpose of uniformly supplying gas onto the semiconductor wafer and thus maintaining a constant concentration of the reactant gas, a method is employed according to which a gas shower unit is positioned directly above the semiconductor wafer, the shower unit being formed of a sheetlike base material with a large number of through holes formed therein. This method enables gas to blow out as if from a showerhead, and consequently the gas concentration can be made as constant as possible on the semiconductor wafer surface.
The temperature at which the gas is caused to react is different depending on the type of reactant gas. Approximately, the temperature is 100 to 400xc2x0 C. for high-temperature etching, 200 to 500xc2x0 C., for plasma CVD and 400 to 800xc2x0 C. for CVD.
Usually the wafer holder has a heater therein to directly heat a wafer and adjust temperature to the one required for reaction. If a reactant gas at room temperature is directly supplied from the gas shower unit, the reactant gas is suddenly heated on the wafer and accordingly the wafer temperature is decreased. Therefore, it is difficult to make the gas temperature constant especially over the surface of a large-area wafer and the reaction rate varies depending on the location on the wafer, so that a film having a uniform thickness is difficult to produce.
Then, a method of preliminary heating a reactant gas may be employed according to which the reactant gas is supplied into a chamber from piping provided outside a semiconductor manufacturing apparatus, and the gas is heated by a heater and then passed through a gas shower unit.
However, if the reactant gas is heated in advance before being passed through the gas shower unit, the reactant gas starts reacting before passing through the through holes of the gas shower unit. A resultant problem is clogging of the through holes of the gas shower unit or wastefully generated reaction products in the pre-heating portion. Another problem is that reaction products peel off to generate particles attaching onto the wafer surface as foreign matters or contaminants.
In order to solve above problems, a heater may be provided in a gas shower unit. If the gas shower unit having a heater therein is produced by providing a heater coil or wire between ceramics compact pieces and hot-press sintering them, the thickness of a base material of the gas shower unit is 10 mm or more because the heater coil embedded within the base material has an outer diameter of approximately 3 to 6 mm. As a result, through holes are likely to clog. Further, since the through holes should be formed not to touch the heater coil, there is a limitation on locations where the through holes are to be made. In this case, in many regions, the interval between through holes is 3 to 6 mm or more. In addition, if the gas shower unit has a greater thickness due to an embedded coil, the through holes are accordingly longer and thus likely to clog as described above.
A further method employed for ensuring uniform heating on a wafer where reaction occurs is that a gas shower unit is warmed by heat radiated from a wafer holder which has a heater therein and is located under a wafer, and after the gas shower unit is warmed to a predetermined temperature, gas is supplied therefrom.
In film deposition, a film is stacked not only on a wafer as a product but also on the gas shower unit, wafer holder and chamber. When the stacked film increases in thickness, thermal stress causes peeling of the film, which generates particles attached onto the product wafer, and accordingly defect occurs. Therefore, the surfaces of components within the chamber should be cleaned frequently. The optimum temperature for film deposition and that for cleaning are different. In general, such a gas as ClF3, NF3 or the like is used for cleaning. Since this type of gas would have too great etching power if used at the film deposition temperature, temperature in cleaning should be made lower than the film deposition temperature so as not to excessively damage the surfaces of the gas shower unit, wafer holder and chamber. Then, the temperature should be changed in the course from film deposition (high temperature), cleaning flow temperature), then to film deposition (high temperature) and so on. The gas shower unit having no heater therein is heated only by heat radiated from the heater located below and accordingly takes a considerable time to reach a predetermined temperature. In this case, the incorporated cleaning process constitutes a main factor in decrease of throughput in wafer processing.
One object of the present invention is to provide a gas shower unit for a semiconductor manufacturing apparatus and to provide a semiconductor manufacturing apparatus including therein the gas shower unit, to enable reaction to occur uniformly within a chamber of the semiconductor manufacturing apparatus such as CVD apparatus, plasma CVD apparatus, etching apparatus and the like while overcoming the problems above.
Another object of the invention is to provide a gas shower unit for a semiconductor manufacturing apparatus and to provide a semiconductor manufacturing apparatus including therein the gas shower unit, in which clogging of through holes hardly occurs in the gas shower unit of a thin type and in which a cleaning step can readily be done even when unnecessary films which could cause clogging or produce particles are deposited on the surfaces of components within a chamber of the semiconductor manufacturing apparatus, thus increasing throughput in wafer processing.
A gas shower unit for a semiconductor manufacturing apparatus according to the present invention has a base material of 5 mm or less in thickness, and includes a sintered ceramics base material having a plurality of through holes and an electrically conductive layer formed in the sintered ceramics base material.
A desirable gas shower unit for decreasing the frequency of cleaning steps has through holes which are not clogged for at least 24 hours. A gas shower unit can be employed which includes a base material of 5 mm or less in thickness with through holes each of a normal diameter (at least 0.01 mm) in order to prevent the through holes from being clogged for at least 24 hours. Accordingly, if the gas shower unit according to the present invention is employed, through holes hardly clog in the thin gas shower unit, and preliminary heating, which could cause clogging of the through holes, is unnecessary. Further, the heater can be included as the conductive layer in the gas shower unit so as to smoothly increase temperature, from a lower one at which cleaning is done for removing a deposited film attached to chamber components that generates particles, to a higher one at which a film is deposited on a wafer, and accordingly throughput in wafer processing can be enhanced. A desirable time period required to increase and decrease temperature is one hour or less in total. Including of the heater can reduce the time for increasing the temperature, and forming of a gas shower unit into a thin shape can reduce the time for decreasing the temperature.
Preferably, in consideration of uniform reaction, the gas shower unit according to the present invention includes an electrically conductive layer where a heater circuit pattern is formed. Accordingly, reactant gas is preliminarily heated when it passes through holes of the gas shower unit so that reaction uniformly occurs in a chamber for a semiconductor manufacturing apparatus. Occurrence of through hole clogging as well as generation of particles can thus be avoided.
Preferably, the electrically conductive layer of the gas shower unit according to the present invention includes an electrically conductive layer in which an electrode for generating plasma is formed. In this way, any space between a plasma upper electrode and the gas shower unit can be eliminated to obtain uniform plasma so that reaction can be made uniform within a chamber for a semiconductor manufacturing apparatus. It is thus possible to prevent clogging of through holes as well as generation of particles due to unnecessary films which might be formed in such a space as above.
Preferably, the sintered ceramics base material of the gas shower unit according to the present invention has at least 0.1 through holes per square centimeter each having a diameter of 0.01 mm or more. More preferably, the sintered ceramics base material has at least 0.5 through holes per square centimeter each having a diameter of 0.01 mm or more. The dimension and density of the above numerical values of through holes enables reactant gas to be supplied uniformly onto a semiconductor wafer within a chamber of a semiconductor manufacturing apparatus. Accordingly, temperature distribution over the semiconductor wafer can be made more uniform.
Ceramics used for the base material constituting the gas shower unit according to the present invention preferably includes any one of aluminum nitride, aluminum oxide, silicon nitride and aluminum oxynitride. The aluminum nitride is most preferred because of its heat conductivity and corrosion resistance. Such a ceramics material provides the base material of the gas shower unit with heat resistance as well as corrosion resistance against corrosive gas containing halogen, for example, used as a reactant gas.
Preferably, in the gas shower unit according to the present invention, the sintered ceramics base material includes a first sintered ceramics piece and a second sintered ceramics piece and the electrically conductive layer is preferably formed on a surface of the first sintered ceramics piece. The gas shower unit of the present invention preferably includes a joint layer interposed between the surface of the first sintered ceramics piece having the electrically conductive layer formed thereon and the second sintered ceramics piece, for coupling the first and second sintered ceramics pieces.
The gas shower unit of the present invention may be structured by forming a conductive layer on one surface or both surfaces of a sintered ceramics base material and forming a protective layer to cover a surface of the conductive layer. In one specific embodiment, a gas shower unit including a heater circuit therein may have a structure in which only one sintered ceramics piece is used as the sintered ceramics base material, a conductive layer is formed as a heater circuit pattern on one surface of the sintered ceramics piece, and a surface of the conductive layer is covered with a protective layer having a high corrosion resistance, preferably a protective layer formed of nonoxide ceramics in order to protect the conductive layer from corrosive gas such as halogen and the like. Alternatively, a gas shower unit including therein a heater circuit and a plasma upper electrode may have a structure in which only one sintered ceramics piece is used as the sintered ceramics base material, a conductive layer is formed as a heater circuit pattern on one surface of the sintered ceramics piece, a conductive layer is formed as a plasma upper electrode on the other surface of the sintered ceramics piece, and the surfaces of the conductive layers formed respectively on both surfaces of the sintered ceramics piece are covered with a protective layer having a high corrosion resistance, preferably a protective layer formed of nonoxide ceramics in order to protect the conductive layers from corrosive gas such as halogen and the like. In each of the gas shower units above, joining of sintered ceramics pieces is unnecessary and accordingly, factors causing defects such as joint gap can be reduced and yield can be increased. Further, since the gas shower unit is constituted using one sintered piece which reduces manufacturing cost.
The joint layer or protective layer preferably includes glass. If the gas shower unit is used at a high temperature with a high voltage applied thereto, the joint layer or protective layer more preferably includes nonoxide ceramics in terms of heat resistance, corrosion resistance and voltage resistance. In this case, the nonoxide ceramics preferably includes at least 50% by mass of any of aluminum nitride and silicon nitride.
If any of aluminum nitride, aluminum oxide, silicon nitride and aluminum oxynitride is used as ceramics constituting the base material, the joint layer above is preferably a glass layer having a coefficient of thermal expansion of at least 3.0xc3x9710xe2x88x926/xc2x0C. and at most 8.0xc3x9710xe2x88x926/xc2x0C. Use of such a glass layer as the joint layer enables the thermal expansion coefficient of the joint layer to be almost equal to that of the sintered ceramics piece. Consequently, thermal stress generated in joining, or heating and cooling of the gas shower unit can be decreased.
As the protective layer above, a glass having corrosion resistance as high as possible is preferably used. In consideration of reduction of thermal stress, the protective layer is preferably a glass layer having a thermal expansion coefficient of at least 3.0xc3x9710xe2x88x926/xc2x0C. and at most 8.0xc3x9710xe2x88x926/xc2x0C. The target time for heating the gas shower unit from room temperature to 600xc2x0 C. is 30 minutes or less. If the thermal expansion coefficient falls in the range above, this target can be achieved.
If aluminum nitride is used as ceramics constituting the base material, in consideration of wetting and bonding properties, the joint layer including glass preferably includes oxide containing ytterbium (Yb), neodymium (Nd) and calcium (Ca) or includes a compound which generates oxide containing ytterbium (Yb), neodymium (Nd) and calcium (Ca) by being heated. If ceramics constituting the base material is silicon nitride, in consideration of wetting and bonding properties, the joint layer including glass preferably includes oxide containing yttrium (Y) and aluminum (Al) or includes a compound which generates oxide containing yttrium (Y) and aluminum (Al) by being heated.
If nonoxide ceramics is used as a material for the joint layer or protective layer, in consideration of thermal stress, nonoxide ceramics having a thermal expansion coefficient of at least 3.0xc3x9710xe2x88x926/xc2x0C. and at most 6.0xc3x9710xe2x88x926/xc2x0C. is preferably used.
Preferably, the conductive layer in the gas shower unit according to the present invention includes at least one of tungsten, molybdenum, silver, palladium, platinum, nickel and chromium.
Preferably, the conductive layer in the gas shower unit according to the present invention is formed along a plane within the sintered ceramics base material. Further, the gas shower unit preferably includes an external connection terminal which is formed along the same plane as that in the sintered ceramics base material to connect to the conductive layer and exposed from the sintered ceramics base material. It is accordingly possible to expose to reactant gas only the region of the sintered ceramics base material including the conductive layer therein and to locate the external connection terminal outside a chamber of a semiconductor manufacturing apparatus. Since the conductive layer included in the sintered ceramics base material and the external connection terminal coupled to the conductive layer are formed along the same plane, uniform heating of the gas shower unit as well as shortening of time period required for heating and cooling are possible. In other words, heating and cooling rates can be enhanced.
Preferably, the gas shower unit according to the invention further includes a temperature detection unit included in the sintered ceramics base material. Temperature distribution in the gas shower unit can thus be measured to control heating temperature of the gas shower unit.
A semiconductor manufacturing apparatus according to the present invention includes therein the semiconductor manufacturing apparatus gas shower unit structured in the above-described manner.
The semiconductor manufacturing apparatus according to the present invention is one selected from the group consisting of etching apparatus, CVD apparatus and plasma CVD apparatus.
According to the present invention, it is possible to provide, as a gas shower unit used for a semiconductor manufacturing apparatus such as CVD apparatus, plasma CVD apparatus, high temperature etching apparatus and the like where heating should be done more uniformly because of increased outer diameter of a semiconductor wafer to be processed, a structure having a heater function or a structure having both of the heater and plasma electrode functions. Use of a gas shower unit having such a structure enables reactant gas to be heated uniformly, and accordingly enables film deposition or etching to be done uniformly on a semiconductor wafer surface. In addition, there is generated no unnecessary film on the surface of the base material of the gas shower unit, and thus it is possible to prevent the concentration and flow rate of gas within a chamber from changing with time due to dogging of through holes. Further, it is possible to prevent particles from being generated resulting from peeling of a film attached to the surface of the base material of the gas shower unit.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.